proc_macro: consolidate bridge::client::run_expand{1,2} into one helper.
proc_macro: consolidate bridge::client::run_expand{1,2} into one helper.

graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust